The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions.
The advantages of employing broadband amplifiers that selectively apply electrical power to increase the output strength of input signals received within pre-specified frequency bands are desirable in many areas of electrical and electronic systems design, fabrication and use. In communications system technology, offered as one example and not intended as a limitation of the scope of the method of the present invention, the use of power amplifiers in transceiver architectures that provide signal amplification in frequency bands especially suited for the intended purpose of a system embodying a particular transceiver architecture offers many advantages. Firstly, the performance advantage of increasing signal strength primarily or essentially only in those frequency bands of interest to an intended user can be improved by knowledgeable power amplifier design. Secondly, conserving electrical power by expending energy primarily in providing the most desired output signal frequency bands reduces energy wastage, reduces cost of operations, and extends the time of effectiveness of an electrical battery or a capacitive source of electrical energy. Additional parameters of interest in a power amplifier design include (a.) reducing cost of components of the power amplifier circuit; (b.) reducing the required footprint and operating volume of the desired power amplifier circuit within its comprising system; (c.) imposing modest or little challenge in manufacturability of the desired power amplifier circuit within its comprising system; and (d.) imposing lower insertion loss performance by the desired power amplifier circuit upon its comprising system. It is understood that a reduction in insertion loss translates into an increased possible maximum output power, and thereby enables an improvement in overall power efficiency, of the comprising amplifier or transceiver.
Broadband power amplifiers in wireless communications systems preferably present transistor power matching over large frequency ranges. Furthermore, it is generally desirable in electronic systems adapted to transmit radio waves that a power amplifier present an impedance match having a radio characteristic impedance, e.g., 50 ohm or 75 ohm, to any coupled transistor impedance, wherein the target impedance is usually low ohmic due that may be caused by a high capacitive impedance resulting from by a relatively large transistor having a high drain current.
Prior art power amplifiers often use transformer topologies to generate a 180° phase shift and provide impedance matching. The prior art design approach to high frequency and broadband coverage includes applying topologies that include Ruthroff circuits and/or Guanella structures. These prior art circuits are usually used for broadband transform and deliver a four to ten impedance value obtained with a penalty up to 2 dB of insertion losses.
Some prior art alternatives provide cascaded transformers intended to optimize the phase shift in a first stage and then a transformer impedance characteristic in a second stage. As the mains terminal capacitors cause a low ohmic impedance of the power amplifier transistors, some designs use cascade structures to reduce the input or output capacitor in reliance upon the well-known Miller effect. The total resulting impedance of prior art power amplifiers may then be improved by introduction and use of a feedback network which reduces the power gain of the amplifier.
The prior art fails to offer optimized power amplifier designs that apply band pass filtering techniques and circuits that at least partially compensate for any performance effect imposed by the inclusion of simplified transformer elements within a power amplifier circuit.